No icons and pictures for Contacts on Messages

Hello,

I have pinned 9 contacts on the Message app, with icons and contacts pictures. But regularly some pins picture disappears without any reason, the pins are left with contacts initials only. In order to restore the pins pictures I have to go to the phone contacts make a simulacre of editing the phone contact picture but without changing anything, then the pinned icons pictures are miraculously returned.

Is there any explanation for the phenomenon?

[Re-Titled by Moderator]